The present invention generally relates to an apparatus for optimizing the charging of a rechargeable battery and, in particular, relates to one such apparatus having means for providing a current path for current from a recharging current source when the battery is recharged regardless of the ambient temperature.
Rechargeable batteries have long been employed to avoid the expense of replacing discharged batteries. One of the most common rechargeable batteries is that used in an automobile. The automobile battery, as generally known, is recharged via current supplied from the automobile's generator when the engine is running. When the automobile battery is fully charged a relay, or similar switching device, causes the current flow to the battery to be terminated. The use of a rechargeable battery in an automobile, however, is not only a rather specialized application but also a well defined application wherein, for example, the battery is readily available for external recharging or replacement if the battery is unintentionally fully discharged.
Other, more generalized, applications for rechargeable batteries involve conditions where there is a wide variation in the ambient temperature, where the ability to service such a battery in person is prohibitively expensive due, for example, to the sheer number of units involved or to the remote location thereof, or both. The provision and control of a generator for each, or even a reasonable number of such batteries, under such conditions would usually also be prohibitively expensive. Consequently, some other means must be provided to recharge such batteries.
One conventional solution is to provide a battery charger that operates from a source of electrically near the rechargeable battery, such as the local electrical power main. However, such battery chargers are rather complex constant current or constant voltage sources requiring switching circuitry to regulate and turn off the recharging current to the battery when it is recharged. Further, such battery chargers are usually not suitable for trickle charging a battery and do not compensate for changes in the ambient temperature of the battery. Further, conventional battery chargers are relatively easily bypassed, this is a major consideration when, for example, the battery is used to power a monitor for measuring a consumers use of a utility, such as, water or electricity. In addition, under such circumstances, the consumers would quite probably be very resistant to such an installation if they were to be billed for the power necessary to operate a utilities monitoring device.
Furthermore, due, to a large degree, to the variation of the charging characteristics of rechargeable batteries with changes in the ambient temperature thereof many such rechargeable batteries are frequently overcharged. Although overcharging a rechargeable battery at low currents, i.e., trickle charges, does not usually result in a catastrophic failure of the battery, it does, nevertheless, reduce the useful life of the battery. Over a period of time, such a decreased lifetime can be a significant cost consideration where the number of batteries involved is large.
Consequently, a simplified apparatus for optimizing the trickle charging of a rechargeable battery is highly desirable to both preserve the useful life of the rechargeable battery and to reduce the cost of such a recharging apparatus.